HVAC Duct Design

1. Provider and applicable terms

HVAC Duct Design is provided under the Set In Stone brand by the app provider identified on the App Store listing. Contact [email protected] with “HVAC Duct Design” in the subject. Apple’s Standard End User License Agreement applies to the app license; these additional terms describe what the app does, its limits, and the purchase. Mandatory consumer rights remain unaffected.

2. A calculator, not engineering approval

HVAC Duct Design estimates round duct diameter, rectangular sizes, air velocity, friction rate, velocity pressure, and run pressure drop from the airflow, friction rate or velocity, shapes, lengths, and fittings you enter. It applies the equal-friction relation for round duct at standard air and the Huebscher equivalent for rectangular duct, and it ranks standard sizes by how closely they match your target. Results depend on your inputs and on assumptions that may not match your job, including air density, duct material and roughness, fitting arrangement, and installation conditions.

All values are estimates. The app does not guarantee any airflow, noise level, pressure, comfort, energy, or code-compliance result, and it does not replace a load calculation, a design made to a recognized standard such as ACCA Manual D, ASHRAE, or SMACNA guidance, local code, or the judgment of a licensed professional. Check consequential results independently before you order, fabricate, or install anything. You are responsible for the sizes you choose.

3. Reference tables and fitting values

The Reference tab and the fitting equivalent lengths come from published sources named next to each table in the app, such as articles and guides from HVAC School, Energy Vanguard, and Southwark Metal Mfg. Co. that describe ACCA Manual D values. They are secondary summaries, not the standards themselves, and may differ from the edition you work to. Where a source gives a range, the app uses the high end. A fitting with no value in the table is counted as zero length, and the screen says so.

HVAC Duct Design is not affiliated with, endorsed by, or sponsored by ACCA, ASHRAE, SMACNA, HVAC School, Energy Vanguard, or Southwark Metal Mfg. Co. Their names and marks belong to their owners and appear only to credit sources.

4. Your jobs and information

You keep your rights in the job names, addresses, notes, and run data you create. You are responsible for the information you enter, for having the right to enter it, and for keeping device backups. Jobs are stored locally. Deleting a job or the app can permanently remove it, and we cannot recover local-only data.

The app can create a plain-text summary of a job for you to share. Once you share it, you control where it goes. You are responsible for who you send it to and for any client or site information it contains.

5. Lifetime purchase

HVAC Duct Design is unlocked with a one-time, non-consumable lifetime purchase. It is not a subscription, does not renew, and offers no free trial unless Apple’s purchase confirmation expressly says otherwise. The App Store purchase screen shows the price and currency for your storefront before you confirm, and the app shows the same price. Prices differ by storefront and may change for future buyers. The purchase is not available through Family Sharing.

Lifetime access covers the app features offered under this purchase on the Apple Account used to buy it. It is not a guarantee of indefinite hardware compatibility or of perpetual operation of third-party services such as the App Store or the purchase service. Future paid products, if any, would be offered separately and clearly priced.

6. Restore, refunds, and access changes

Use Restore Purchases on the paywall or in Settings to verify an eligible lifetime purchase made with your Apple Account, for example after reinstalling the app or changing devices. Apple and RevenueCat verify access. Refunded, revoked, or pending purchases may not grant access.

Apple manages payments and App Store refund requests. Use Apple’s billing and refund support at https://support.apple.com/billing. Set In Stone cannot directly issue an App Store refund. Nothing here excludes refund or other consumer rights that apply by law.

7. Availability and responsibility

The app depends on a compatible device, operating-system functionality, and the purchase services. Availability, software defects, and third-party outages may affect operation. We do not describe the app as error-free or suitable for every job or device.

To the extent permitted by applicable law, the app is provided as available and without a guarantee of uninterrupted operation or fitness for a particular design task, and we are not liable for losses that arise from relying on an estimate without independent verification. These terms do not exclude liability or remedies that cannot lawfully be excluded, including mandatory consumer rights, nor require you to waive accrued rights.

8. Privacy and changes

Information processing is described in the HVAC Duct Design Privacy Policy at https://setinst.one/apps/hvac-duct-design/privacy/. Apple, RevenueCat, and linked services operate under their own applicable terms and notices.

These terms are effective October 30, 2026. Material changes will be published with a revised date and additional notice where required. Changes do not retroactively remove accrued rights or alter a completed purchase contrary to law. Contact [email protected] for support or questions.